Summary of Work: Comparison of listed characteristics from representative sections of lung tissue from 7 female rats from each study All will be terminal sacrifice animals without evidence of Mononuclear cell leukemia. Epithelial neoplasms will not be present in the sections. Morphometry and cell counts will be enabled by special stains. (Toluidine blue for mast cells. Amounts and ratios of collagen types and elastin using Verhoeff-van Gieson, Masson's trichrome, Sirius red, and Herovici's picropolychromium stains.) Fibroblast smooth-muscle actin expression, and levels of Transforming Growth Factor-beta expression in the lung would be compared immunohistochemically. PCNA will be used to determine epithelial proliferatation.